1. Field of the Invention
The present invention relates to a technique for recording or reproducing information by irradiating a laser beam onto a disc medium.
2. Description of the Prior Art
At present, an apparatus using an optical disc corresponding to a large capacity removable medium is commercially manufactured as an external information storing apparatus for a personal computer or the like. The apparatus is structured such that a disc medium is mounted to a spindle motor by a loading mechanism provided in an inner portion, an optical pickup for irradiating an optical spot on an information recording surface is provided so as to oppose to the disc medium, and the optical spot is irradiated onto the disc medium so as to record or reproduce a signal. A laser light source, a prism for irradiating a laser beam outgoing from the laser light source onto the disc medium, an optical element such as an objective lens or the like, a light detecting portion for detecting a reflected light from the optical disc so as to convert into an electric signal, an objective lens driving portion for controlling a focal point of a light spot to a target position on the disc recording medium surface, and the like are mounted in the optical pickup mentioned above. The objective lens driving portion is structured such as to finely move the objective lens in a direction of an optical axis in correspondence to a surface deflection amount of the rotating disc medium, and finely move the objective lens in a track direction of the disc medium in correspondence to a track displacement amount. An embodiment of structure of the objective lens driving portion for the optical pickup mentioned above is disclosed in JP-A-6-89448 and the like. In this case, a description will be given below of the objective lens driving portion of the optical pickup which has been conventionally employed, with reference to FIG. 32. In FIG. 32, reference numeral 3201 denotes an objective lens, which is mounted to a front end portion of a lens holder 3202. A focus coil 3203 to which a coil is applied by a copper wire or the like is mounted to an inner portion of the lens holder 3202, and two tracking coils 3204 to which a coil is applied by a copper wire or the like are mounted to an outer side of the focus coil 3203. Two magnets 3205 are provided in the focus coil 3203 and the tracking coil 3204 so as to oppose to each other with a predetermined gap, and the magnets 3205 are mounted to a yoke 3206 made of a magnetic material such as an iron or the like. One ends of four suspensions 3207 are mounted to right and left side surfaces of the lens holder 3202, and the focus coil 3203 and the tracking coil 3204 are electrically connected. Further, the other ends of the suspensions 3207 are mounted to a connection base plate 3209 attached to a suspension holder 3208 in accordance with a soldering or the other means, and right and left side surfaces of the suspension holder 3208 are fixed to a unit base 3211 by an adhesive portion 3210. The yoke 3206 and the unit base 3211 are integrally formed in accordance with a press molding or the other means, and a side surface and a bottom surface in the unit base 3211 are fixed to a casing 3212 by an adhesive portion 3213 after predetermined position and attitude are determined with respect to an optical system (not shown) provided in a casing 3212 of the optical pickup. In this state, the lens holder 3202 including the objective lens 3201 is supported so as to freely move in parallel in a surface deflecting direction (Z direction in this drawing) of the optical disc and a radial direction (Y direction in this drawing), and the structure is made such that a thrust due to an electromagnetic force is applied by controlling so as to apply an electric current to the focus coil 3203 and the tracking coil 3204, whereby the lens holder 3202 is driven in a focus direction (Z direction in this drawing) or a tracking direction (Y direction in this drawing).
The optical disc apparatus described above is, at the present time, mainly used in an aspect of being connected to an information equipment such as a personal computer or the like via a cable, or being installed in the information equipment such as a notebook computer or the like, or the like.
At present, the optical disc apparatus is structured such as to be mainly used in the aspect described in the prior art mentioned above, however, there has been proposed, for example, a portable optical disc camera apparatus (the disc medium employs, for example, a digital versatile disc-random access memory (DVD-RAM)) capable of photographing a digital moving image and static image, as a new type optical disc apparatus in which a microphone for recording an external voice is installed. In the optical disc camera apparatus mentioned above, components such as an imaging system, a recording microphone, an optical disc drive, a signal processing circuit and the like are mounted within a casing, and the recording microphone is arranged close to the optical disc drive for the purpose of making a whole of the apparatus compact. Accordingly, in an operation of the optical disc drive, (1) there is a case that an operation sound having a peak in a frequency band range between some KHz and 10 KHz jumps into the recording microphone, whereby a reproduction sound quality is deteriorated, and (2) there is a case that the operation sound having the peak in the frequency band range between some KHz and 10 KHz leaks from the casing of the apparatus, thereby striking harshly upon the ear.
As a result of considering a reason by which the operation sound is generated, it has been known that one of main reasons by which the operation sound in the band range between some KHz and 10 KHz is generated, exists a matter that in the objective lens driving portion (FIG. 32) of the conventional optical pickup arranged in opposite to the disc surface at a time of a focusing operation mode and a tracking operation mode, the yoke corresponding to the constituting element finely vibrates, the fine vibration is input to the objective lens driving unit via a loop of a focus and tracking servo control system so as to constitute a disturbance, and this state is repeated, whereby the fine vibration is amplified and appears on the operation sound. Further, it has been known that together with dispersion on manufacturing, a rotational vibration which is fined in the lens holder for holding the objective lens is easily generated in the objective lens driving portion (FIG. 32) of the conventional optical pickup, the fine rotational vibration vibrates the yoke and is amplified via the loop of the focus and tracking servo control system so as to appear on the operation sound. At this time, in a frequency characteristic (a response displacement and a phase characteristic) of the focus and tracking servo control system, there is not generated a response turbulence which generates a problem in view of the servo control, and a recording and reproducing operation on the disc is normally executed. As a result of the above, it can be said that no deterioration is generated in the response of the objective lens with respect to the disc, that is, the light spot on the disc surface. In the conventional optical disc apparatus, the turbulence which will generate the problem in view of executing the servo control is not produced in the frequency characteristic (the gain and phase characteristics) of the focus and tracking servo control system, as mentioned above, and the operation sound in the band range between some KHz and 10 KHz which is generated due to the operation of the objective lens driving portion generates a problem hardly produces the problem, in a state in which the recording and reproducing operation on the disc is normally executed.
As mentioned above, in the case that the objective lens driving portion of the optical pickup is operated, the operation sound in the band range between some KHz and 10 KHz which is caused by the fine vibration generated from the yoke corresponding to the constituting element even in the state in which the objective lens and by extension the optical spot normally responds, and the fine rotational vibration generated by the lens holder holding the objective lens due to the dispersion on manufacturing becomes a new problem which is hardly considered in the conventional optical disc apparatus in view of achieving the optical disc camera installing the recording microphone therein. Accordingly, in order to reduce the operation sound in the band range between some KHz and 10 KHz, it is necessary to reduce the operation sound generated from the yoke corresponding to the constituting element of the objective lens driving portion and the rotational vibration of the lens holder holding the objective lens in spite of the dispersion on manufacturing.